a. Field of Invention
This invention relates generally to video monitors and automatic alignment systems for video monitors, particularly automatic alignment systems including a camera for capturing an image of a displayed image on the monitor and accurately computing physical characteristics of the displayed image relative to the monitor by transforming coordinate systems.
b. Description of the Background
During assembly of video monitors, it is necessary to adjust certain parameters of the video monitor to achieve desired displayed characteristics in the displayed image of the monitor. Traditionally, video monitors have been adjusted by skilled operators in the factory prior to shipment to the customer. Manual adjustment of the monitor, however, is fraught with several problems. First of all, manual adjustment has meant manual measurement of physical characteristics of the displayed image, often with a tape measure. Consequently, the accuracy of the measurement and adjustment is greatly dependent upon the skill of the operator. In addition, operator fatigue plays a role in inaccurate adjustments. Third, consistent, objective and repeatable adjustments are unlikely with the manual system.
Another method for measurement of the physical characteristics of the displayed image uses optics and/or a light sensor mounted on an x-y positioning platform. This method can be very accurate but requires precise alignment of the measuring system to the CRT display. This method is also very slow and not applicable for production or manufacturing facilities for monitors where speed of adjustment is a driving factor.
U.S. Pat. No. 5,216,504, issued to the assignee of the present application, discloses an "Automatic Precision Video Monitor Alignment System" and is specifically incorporated herein by reference for all that it discloses and teaches. This system involves a single camera placed in front of a video monitor to capture a displayed image which is then supplied to a video board of a computer for analysis of the physical characteristics of the displayed image. The camera also captures an image of the display bezel which limits the outer boundary of the light-emitting area on the CRT. The bezel may be in the form of a shadow mask, an aperture grill, a display bezel or faceplate, or the like. The four inner corners of the bezel are ascertained and a two-dimensional, interpolative correction is made for camera/monitor misalignment. However, such an approach is limited in its accuracy and angular independence. This is mostly due to the use of a two-dimensional approach to compensate for a three-dimensional geometry of the CRT. Further, there are refraction errors due to the curvature and glass thickness of the CRT. Typically, the monitor manufacturer provides information pertaining to both the thickness and curvature of the glass that comprises the front face of the cathode ray tube monitor so that corrections can be made for refraction. However, it has been found that in many instances this information is not completely correct, or may change slightly over a period of time as changes are made by the manufacturer over a period of time. Even small changes in the amount, or shape, of curvature or thickness, can greatly affect the refraction produced by the front surface of the tube. In some cases, these specifications are not even available from the manufacturer. Moreover, calculation of incident angles for different curvatures can be difficult and subject to error. For these reasons, it is desirable to provide a system that can determine refractive errors for various positions on a cathode ray tube monitor in a simple and easy fashion that can be derived by empirical techniques.
It is against this background and the desire to improve on the prior art techniques that the present invention has been developed.